Bag-in-containers, also referred to as bag-in-bottles or bag-in-boxes depending on the geometry of the outer vessel, all terms considered herein as being comprised within the meaning of the term bag-in-container, are a family of liquid dispensing packaging consisting of an outer container comprising an opening to the atmosphere—the mouth—and which contains a collapsible inner bag joined to said container and opening to the atmosphere at the region of said mouth. The system must comprise at least one vent fluidly connecting the atmosphere to the region between the inner bag and the outer container in order to control the pressure in said region to squeeze the inner bag and thus dispense the liquid contained therein.
Traditionally, bag-in-containers were—and still are—produced by independently producing an inner bag provided with a specific neck closure assembly and a structural container (usually in the form of a bottle). The bag is inserted into the fully formed bottle opening and fixed thereto by means of the neck closure assembly, which comprises one opening to the interior of the bag and vents fluidly connecting the space between bag and bottle to the atmosphere. Examples of such constructions can be found inter alia in U.S. Pat. Nos. 3,484,011, 3,450,254, 4,330,066, and 4,892,230. These types of bag-in-containers have the advantage of being reusable, but they are very expensive and labour-intensive to produce.
More recent developments focused on the production of “integrally blow-moulded bag-in-containers” thus avoiding the labour intensive step of assembling the bag into the container, by blow-moulding a polymeric multilayer preform into a container comprising an inner layer and an outer layer, such that the adhesion between the inner and the outer layers of the thus produced container is sufficiently weak to readily delaminate upon introduction of a gas at the interface. The “inner layer” and “outer layer” may each consist of a single layer or a plurality of layers, but can in any case readily be identified, at least upon delamination. Said technology involves many challenges and many alternative solutions were proposed.
The multilayer preform may be extruded or injection moulded (cf. U.S. Pat. No. 6,238,201, JPA10128833, JPA11010719, JPA9208688, U.S. Pat. No. 6,649,121. When the former method is advantageous in terms of productivity, the latter is preferable when wall thickness accuracy is required, typically in containers for dispensing beverage.
The formation of the vents fluidly connecting the space or interface between bag and bottle to the atmosphere remains a critical step in integrally blow-moulded bag-in-containers and several solutions were proposed in e.g., U.S. Pat. Nos. 5,301,838, 5,407,629, JPA5213373, JPA8001761, EPA1356915, U.S. Pat. No. 6,649,121, JPA10180853.
One redundant problem with integrally blow-moulded bag-in-containers is the choice of materials for the inner and outer layers which must be selected according to strict criteria of compatibility in terms of processing on the one hand and, on the other hand, of incompatibility in terms of adhesion. These criteria are sometimes difficult to fulfill in combination as illustrated below. This problem does not arise in the field of blow-moulding co-layer plastic containers, wherein the adhesion between layers is maximized in order to avoid delamination, because best adhesion is obtained with similar materials, which generally have similar thermal properties. Consequently, finding materials being compatible in terms of both processing and adhesion as for the fabrication of co-layer containers is generally less problematic than finding materials being compatible in terms of processing and incompatible in terms of adhesion as for the fabrication of bag-in-containers.
Addressing processing compatibility, EPA1356915 and U.S. Pat. No. 6,649,121 proposed that the melting temperature of the outer layer should be higher than the one of the inner layer in order to allow production of integral preforms by injection moulding the outer layer first, followed by injecting thereover the inner layer. Examples of materials for the outer layer given by the authors include PET and EVOH, whilst polyethylene is given as an example for the inner layer. Though this materials selection could result advantageous for the injection moulding production of the preforms, it is far from optimal for the blow-moulding step since polyethylene and PET are characterized by quite different blow-moulding temperatures. Again, in U.S. Pat. No. 6,238,201 a method is described including co-extruding a two layer parison followed by blow-moulding said parison into a bag-in-container wherein the outer layer preferably comprises an olefin and the inner layer an amorphous polyimide.
Concerning the materials choice for a weak interfacial adhesion required for ensuring proper delamination of the inner layer from the outer layer upon use, mention is made in JPA2005047172 of “mutually non-adhesive synthetic resins.” In the review of the background art in U.S. Pat. No. 5,921,416 the use of release layers interleafed between inner and outer layers, forming three- or five-layer structures is mentioned. An example of such construction is described in U.S. Pat. No. 5,301,838 which discloses a complex five layer preform comprising three PET layers interleafed by two thin layers of a material selected from the group of EVOH, PP, PE, PA6. Here again, beside the complexity involved with the production of such preforms, substantial differences in blow-moulding temperatures characterize these different materials.
Alternatively and surprisingly it has been discovered that excellent delamination results between the inner and outer layers can be obtained also with preforms wherein both inner and outer layers consist of the same material. Similar results were obtained both with preform assemblies as well as with integral preforms. In the case of integral, over-moulded preforms, it is generally believed that better results are obtained with semi-crystalline polymers.
The same polymer is considered in contact on either side of the interface between the inner and outer layers in the following cases:                inner and outer layers consist of the same material (e.g., PETinner−PETouter, regardless of the specific grade of each PET); or        the inner and outer layers consist of a blend or copolymer having at least one polymer in common, provided said polymer in common is at the interface, whilst the differing polymer is substantially absent of said interface (e.g., (0.85 PET+0.15 PA6)inner(0.8 PET+0.2 PE)outer.The presence in a layer of low amounts of additives is not regarded as rendering the material different, so far as they do not alter the interface substantially.        
Although in case the same material is used for the inner and outer layers, there is no difference in blow-moulding temperature between layers, the heating rate of the two layers can be substantially different due to the wide difference in thicknesses between the inner and outer layers. Moreover, the inner layer is sheltered by the thick, outer layer from the IR-radiation of the IR-oven usually used to bring the preform to blow-moulding temperature. It follows that even for materials having little or no difference in blow-moulding temperature, there can be a problem to heat up simultaneously both layers to their process temperatures.
In order to overcome the problem of different blow-moulding temperatures or heating rates of the materials forming the inner and outer layers of blow-moulded multilayer containers, the different preform components may be heated separately in different ovens to heat them at their respective blow-moulding temperature (cf. e.g., JPA57174221). This solution, however, is expensive in terms of equipment and space and does not apply to integral preforms, which inner and outer layers cannot be separated.
The use of energy absorbing additives in preforms for blow-moulding monolayer containers has been proposed for shortening the heating stage and thus saving energy in, e.g., U.S. Pat. Nos. 5,925,710, 6,503,586, 6,034,167, 4,250,078, 6,197,851, 4,476,272, 5,529,744, and the likes. The use of energy absorbing additives has also been proposed in the inner layer of blow-moulded co-layer containers (i.e., not meant to delaminate) to compensate for the greater strain undergone by the inner layer compared with the outer layer during blow-moulding operation. In co-layer containers it is very important that the inner layer is allowed to stretch sufficiently to contact and adhere to the outer layer over substantially the whole of their interface. The inner layer containing the energy absorbing additives is thus heated to a higher temperature than the outer layer and can be stretched further to adhere to the outer layer.
The above considerations do not apply in the field of bag-in-containers, since a good adhesion between the inner and outer layers is exactly what is to be avoided. Furthermore, preforms for the production of integrally blow-moulded bag-in-containers clearly differ from preforms for the production of blow-moulded co-layered containers, wherein the various layers of the container are not meant to delaminate, in the thickness of the layers. A bag-in-container is comprised of an outer structural envelope containing a flexible, collapsible bag. It follows that the outer layer of the container is substantially thicker than the inner bag. This same relationship can of course be found in the preforms as well, which are characterized by an outer layer being substantially thicker than the inner layer. This has a detrimental effect on the heating efficacy of IR-lamps on heating the inner layer, since the latter is separated from the IR-lamps by the thick wall of the outer layer.
It follows from the foregoing that there remains a need in the art for solutions for compensating the difference in blow-moulding temperatures and heating rates between the “mutually non-adhesive synthetic resins” (cf. JP2005047172) of the inner and outer layers of a preform for the production of integrally blow-moulded bag-in-containers.